| #!/usr/bin/python |
| # Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file |
| # for details. All rights reserved. Use of this source code is governed by a |
| # BSD-style license that can be found in the LICENSE file. |
| |
| """Templating to help generate structured text.""" |
| |
| import logging |
| import re |
| |
| _logger = logging.getLogger('emitter') |
| |
| |
| def Format(template, **parameters): |
| """Create a string using the same template syntax as Emitter.Emit.""" |
| e = Emitter() |
| e._Emit(template, parameters) |
| return ''.join(e.Fragments()) |
| |
| |
| class Emitter(object): |
| """An Emitter collects string fragments to be assembled into a single string. |
| """ |
| |
| def __init__(self, bindings=None): |
| self._items = [] # A new list |
| self._bindings = bindings or Emitter.Frame({}, None) |
| |
| def EmitRaw(self, item): |
| """Emits literal string with no substitition.""" |
| self._items.append(item) |
| |
| def Emit(self, template_source, **parameters): |
| """Emits a template, substituting named parameters and returning emitters to |
| fill the named holes. |
| |
| Ordinary substitution occurs at $NAME or $(NAME). If there is no parameter |
| called NAME, the text is left as-is. So long as you don't bind FOO as a |
| parameter, $FOO in the template will pass through to the generated text. |
| |
| Substitution of $?NAME and $(?NAME) yields an empty string if NAME is not a |
| parameter. |
| |
| Values passed as named parameters should be strings or simple integral |
| values (int or long). |
| |
| Named holes are created at $!NAME or $(!NAME). A hole marks a position in |
| the template that may be filled in later. An Emitter is returned for each |
| named hole in the template. The holes are filled by emitting to the |
| corresponding emitter. |
| |
| Emit returns either a single Emitter if the template contains one hole or a |
| tuple of emitters for several holes, in the order that the holes occur in |
| the template. |
| |
| The emitters for the holes remember the parameters passed to the initial |
| call to Emit. Holes can be used to provide a binding context. |
| """ |
| return self._Emit(template_source, parameters) |
| |
| def _Emit(self, template_source, parameters): |
| """Implementation of Emit, with map in place of named parameters.""" |
| template = self._ParseTemplate(template_source) |
| |
| parameter_bindings = self._bindings.Extend(parameters) |
| |
| hole_names = template._holes |
| |
| if hole_names: |
| hole_map = {} |
| replacements = {} |
| for name in hole_names: |
| emitter = Emitter(parameter_bindings) |
| replacements[name] = emitter._items |
| hole_map[name] = emitter |
| full_bindings = parameter_bindings.Extend(replacements) |
| else: |
| full_bindings = parameter_bindings |
| |
| self._ApplyTemplate(template, full_bindings) |
| |
| # Return None, a singleton or tuple of the hole names. |
| if not hole_names: |
| return None |
| if len(hole_names) == 1: |
| return hole_map[hole_names[0]] |
| else: |
| return tuple(hole_map[name] for name in hole_names) |
| |
| def Fragments(self): |
| """Returns a list of all the string fragments emitted.""" |
| def _FlattenTo(item, output): |
| if isinstance(item, list): |
| for subitem in item: |
| _FlattenTo(subitem, output) |
| elif isinstance(item, Emitter.DeferredLookup): |
| value = item._environment.Lookup(item._lookup._name, |
| item._lookup._value_if_missing) |
| _FlattenTo(value, output) |
| else: |
| output.append(str(item)) |
| |
| output = [] |
| _FlattenTo(self._items, output) |
| return output |
| |
| def Bind(self, var, template_source, **parameters): |
| """Adds a binding for var to this emitter.""" |
| template = self._ParseTemplate(template_source) |
| if template._holes: |
| raise RuntimeError('Cannot have holes in Emitter.Bind') |
| bindings = self._bindings.Extend(parameters) |
| value = Emitter(bindings) |
| value._ApplyTemplate(template, bindings) |
| self._bindings = self._bindings.Extend({var: value._items}) |
| return value |
| |
| def _ParseTemplate(self, source): |
| """Converts the template string into a Template object.""" |
| # TODO(sra): Cache the parsing. |
| items = [] |
| holes = [] |
| |
| # Break source into a sequence of text fragments and substitution lookups. |
| pos = 0 |
| while True: |
| match = Emitter._SUBST_RE.search(source, pos) |
| if not match: |
| items.append(source[pos:]) |
| break |
| text_fragment = source[pos : match.start()] |
| if text_fragment: |
| items.append(text_fragment) |
| pos = match.end() |
| term = match.group() |
| name = match.group(1) or match.group(2) # $NAME and $(NAME) |
| if name: |
| item = Emitter.Lookup(name, term, term) |
| items.append(item) |
| continue |
| name = match.group(3) or match.group(4) # $!NAME and $(!NAME) |
| if name: |
| item = Emitter.Lookup(name, term, term) |
| items.append(item) |
| holes.append(name) |
| continue |
| name = match.group(5) or match.group(6) # $?NAME and $(?NAME) |
| if name: |
| item = Emitter.Lookup(name, term, '') |
| items.append(item) |
| holes.append(name) |
| continue |
| raise RuntimeError('Unexpected group') |
| |
| if len(holes) != len(set(holes)): |
| raise RuntimeError('Cannot have repeated holes %s' % holes) |
| return Emitter.Template(items, holes) |
| |
| _SUBST_RE = re.compile( |
| # $FOO $(FOO) $!FOO $(!FOO) $?FOO $(?FOO) |
| r'\$(\w+)|\$\((\w+)\)|\$!(\w+)|\$\(!(\w+)\)|\$\?(\w+)|\$\(\?(\w+)\)') |
| |
| def _ApplyTemplate(self, template, bindings): |
| """Emits the items from the parsed template.""" |
| result = [] |
| for item in template._items: |
| if isinstance(item, str): |
| if item: |
| result.append(item) |
| elif isinstance(item, Emitter.Lookup): |
| # Bind lookup to the current environment (bindings) |
| # TODO(sra): More space efficient to do direct lookup. |
| result.append(Emitter.DeferredLookup(item, bindings)) |
| else: |
| raise RuntimeError('Unexpected template element') |
| # Collected fragments are in a sublist, so self._items contains one element |
| # (sublist) per template application. |
| self._items.append(result) |
| |
| class Lookup(object): |
| """An element of a parsed template.""" |
| def __init__(self, name, original, default): |
| self._name = name |
| self._original = original |
| self._value_if_missing = default |
| |
| class DeferredLookup(object): |
| """A lookup operation that is deferred until final string generation.""" |
| # TODO(sra): A deferred lookup will be useful when we add expansions that |
| # have behaviour condtional on the contents, e.g. adding separators between |
| # a list of items. |
| def __init__(self, lookup, environment): |
| self._lookup = lookup |
| self._environment = environment |
| |
| class Template(object): |
| """A parsed template.""" |
| def __init__(self, items, holes): |
| self._items = items # strings and lookups |
| self._holes = holes |
| |
| |
| class Frame(object): |
| """A Frame is a set of bindings derived from a parent.""" |
| def __init__(self, map, parent): |
| self._map = map |
| self._parent = parent |
| |
| def Lookup(self, name, default): |
| if name in self._map: |
| return self._map[name] |
| if self._parent: |
| return self._parent.Lookup(name, default) |
| return default |
| |
| def Extend(self, map): |
| return Emitter.Frame(map, self) |
